Dryer-added fabric conditioning products provide a better convenience to the consumer as compared to the rinse-added fabric conditioning products because they spare the consumer the requirement of having to be present right at the beginning of the rinse cycle.
There are two main types of dryer-added fabric conditioning products, namely, single use products and multiple-use products. Single use products, most commonly in the sheet form coated with a fabric conditioning active composition, calls for adding a single sheet into an automatic clothes dryer containing a wet laundry load, at the beginning of the drying cycle. Examples of this type of product are disclosed in U.S. Pat. No. 3,442,692 to Gaiser and U.S. Pat. No. 3,686,025 to Morton et al.
Multiple-use fabric conditioning products are placed in the interior of the dryer to release the fabric conditioning active to successive laundry loads. Each multiple-use product lasts many drying cycles, from a few cycles to about 50 or more cycles, and thus provides a better convenience to the consumer than single use products. Said product can either be an unattached article that is added to an automatic clothes dryer and is tumbled along with a wet laundry load, or an article that is releasably attached to the interior of an automatic dryer drum. An example of an unattached multiple use fabric conditioning article is disclosed in U.S. Pat. No. 3,676,199 issued Jul. 11, 1972 to Hewitt et al.
Another type of multiple-use products consists of a dispenser that is attached to the interior of an automatic clothes dryer to dispense a fabric conditioning active to successive laundry loads. Said dispenser can have a permeable surface and containing a fabric conditioning block that is softenable at the operating temperature of said clothes dryer, as is disclosed, e.g., in U.S. Pat. No. 3,967,008 issued Jun. 29, 1976 and U.S. Pat. No. 4,004,685 issued Jan. 25, 1977, both to Mizuno et al., and U.S. Pat. No. 4,149,977 issued Apr. 17, 1979 to Morganson et al. A preferred type of multiple-use products has the conditioning active not covered by a permeable surface, but is instead exposed to be transferred to the fabric. The product is attached to the interior of the dryer, as disclosed in U.S. Pat. No. 3,696,034 issued Oct. 3, 1972, U.S. Pat. Appl. Publ. No. 2003/0192197 A1 published Oct. 16, 2003 to Griese et al., and U.S. Pat. Appl. Publ. No. 2003/0195130 A1 published Oct. 16, 2003 to Lentsch et al. The softener active, which is solid at room temperature, only softens at a temperature above the clothes dryer operating temperature, as is disclosed in U.S. Pat. Appl. Publ. Nos. 2003/0192197 and 2003/0195130 A1.
While the multiple-use dryer-added conditioning products disclosed in the art can provide an improved convenience, they do have some performance issues. One continuing problem is the varying amount of conditioning active that is released to the fabric, as a function of number of cycles that the products have been used. For instance, U.S. Pat. No. 4,149,977 discusses the need to control the dispensing rate or the consumption rate (Col. 6-8). One means that can be used to regulate the dispensing rate is to select an appropriate conditioning composition, as disclosed in U.S. Pat. No. 4,149,977, issued Apr. 17, 1979 to Morganson et al. U.S. Pat. Appl. Publ. No. 2003/0192197 discloses that the product releases the most active in the earlier drying cycles, and the shape of the product affects the dispensing rate of the product (FIG. 20, and sections [0059] to [0061]). It discloses that a product with a softener block having square edges dispenses more conditioning active at the initial drying cycles than a product with a softener block having rounded edges, thus a product with rounded edges is more preferred to provide a more even dispensing from cycle to cycle, even though the difference between the initial cycles and the late cycles is still very substantial.
There still is a need for further improving the release rate of the fabric conditioning active from cycle to cycle of the multiple use fabric conditioning block.